The present invention relates to concrete slab construction and, more particularly, to methods, apparatuses, and systems directed toward concrete joint restraining systems using pipe dowel mechanisms.
It is well known that concrete expands and contracts due to changes in temperature and moisture. In addition, concrete also contracts as a result of the curing process. In these instances stresses develop that can lead to cracking. Indeed, because concrete slabs can experience large temperature changes over the course of a calendar year, accommodations must be made for the resulting expansion and contraction of the concrete. The thermal expansion and contraction of the concrete under these conditions can prove destructive, leading to undesirable cracking and surface discontinuities if preventive measures are not taken.
To address these problems, engineers employ joints or spacing between concrete slab sections to accommodate thermal expansion and contraction of the concrete. Transverse joints can be saw cut, placed through induced cracking, or formed at pre-determined spacings. Strategic placement of the joints facilitates control of the direction of the expansion and the location where the concrete will crack as a result of the curing process and/or subsequent expansion and contraction. The use of joints or spacing between concrete slab sections, however, has associated problems. Uneven expansion or contraction of the individual sections can result in discontinuities in the slab which, in turn, can lead to unsatisfactory conditions, as well as stress and fatigue in the individual sections. For instance, individual sections can rise or shift relative to adjacent sections to create an uneven surface. To solve this problem, engineers have used dowel bars placed longitudinally in the sections to allow the concrete sections to expand in the longitudinal direction but resist uneven expansion between adjacent sections in the traverse direction of the dowels. For example, by controlling expansion of the sections, engineers can prevent the upper surface of the pavement from becoming discontinuous and uneven.
In addition, it is common to attach the smooth dowels at various points in the rebar matrix that reinforces the concrete. Specifically, before a concrete slab is poured, a rebar matrix is constructed over the desired location (or grade) of the concrete slab. In one form, a rebar matrix is assembled for the entire intended area of the slab. Then, sections of rebar are cut from the matrix, both in the longitudinal and lateral directions, to create a plurality of adjacent rebar matrix sections each having several rebar members extending therefrom in substantial alignment with rebar members of adjacent sections, but spaced apart at a distance determined by the length of the removed sections. Steel dowels are then tied to the substantially aligned rebar sections to span the respective gaps created by the removed sections. The concrete is then poured starting with one section and then moving to adjacent sections until the entire concrete slab is poured. However, this technique has problems beyond the labor intensive nature of tying a large number dowels to the exposed rebar members. Alignment of adjacent dowel bars in a parallel orientation in each section is critical to proper movement of the concrete sections. The tied dowels, however, often become misaligned as trucks and other equipment run over the rebar matrix, and/or as rebar matrix sections are raised during pouring of the concrete, such as with the laser screeding method. Indeed, the tied dowels often become misaligned due to the tie wires breaking and/or due to bending of the rebar members to which the dowels are attached. Moreover, the use of steel dowels often requires the use of protective coatings to ensure that the concrete does not adhere to the dowel and, thereby, prevent slippage of the concrete over the dowel during expansion and contraction. One prior art method is to coat the steel dowels with grease or the like. This process is both messy and time consuming.
In light of the foregoing, a need exists for methods, apparatuses and systems that provide a dowel mechanism for concrete slab construction that solves the problems identified above.
The present invention provides methods, apparatuses and systems directed to joint restraining systems for concrete constructions. The present invention employs a pipe dowel that eliminates many of the problems in the prior art identified above. In one embodiment, the present invention is a novel method for creating joint restraints that employs a pipe dowel. As more fully described below, the present invention substantially reduces the time and labor involved in fixing smooth dowels into a rebar matrix. For example, the present invention eliminates the need to cut out sections of rebar. Rather, embodiments of the present invention require only a single cut in each rebar section along the line of the intended joint, rather than two cuts to remove a section of rebar. The present invention also eliminates the time and effort associated with tying dowels into the rebar matrix. In another embodiment, the present invention is a novel pipe dowel mechanism that, in addition to the advantages described above, obviates the need to apply a protective coating, such as grease, to a smooth dowel. Moreover, the present invention reduces the potential for misalignment of the dowels as the rebar matrix is manipulated and otherwise disturbed during a concrete pour.
The pipe dowel and associated methods of the present invention can be used in any application requiring dowels used in concrete joints, including control and construction joints. For example, the present invention has especial application to any controlled slab on grade pour for which dowels are called. Moreover, the present invention has application in a variety of concrete construction methods. For example, the present invention can be incorporated into processed involving laser screeding, Texas screeding, hand rod screeding, and vibration screeding.